E-mail header injection vulnerabilities

E-mail Header Injection vulnerability is a class of vulnerability that can occur in web applications that use user input to construct e-mail messages. E-mail Header Injection is possible when the mailing script fails to check for the presence of e-mail headers in user input (either form fields or URL parameters). The vulnerability exists in the reference implementation of the built-in mail functionality in popular languages such as PHP, Java, Python, and Ruby. With the proper injection string, this vulnerability can be exploited to inject additional headers, modify existing headers, and alter the content of the e-mail.